Stereo instrument having differentially varied left and right parallax error signals for producing scanning pattern displacements

ABSTRACT

An automatic stereoplotting system employing both a high speed primary servo-system for inducing substantially instantaneous primary relative displacements between scanning patterns to eliminate detected parallax, and a more massive and slower reacting auxiliary servo system for inducing relative displacements between left and right stereo photographs being scanned. The auxiliary displacements of the photographs replace the initial primary displacements of the scanning patterns and a readout mechanism records measured elevations by continuously indicating the algebraic summations of both the primary and auxiliary displacements. A distribution circuit is provided for distributing the displacements of the scanning patterns between the scanning systems for the left and right stereo photographs so as to eliminate the parallax from each photograph in proportion to the actual image displacement on each photograph. This invention is an improvement on the Automatic Stereoplotting Apparatus described in U.S. Pat. No. 3,677,645, filed Mar. 1, 1970.

United States Patent [191 Hardy [11] 3,752,580 [451 Aug. 14, 1973 STEREOINSTRUMENT HAVING DIFFERENTIALLY VARIED LEFI AND RIGHT PARALLAX ERRORSIGNALS FOR PRODUCING SCANNING PATTERN DISPLACEMENTS Inventor: John W.Hardy, Lexington, Mass.

Itelt Corporation, Lexington, Mass.

Oct. 20, 1971 Int. Cl Glc 11/12 Field of Search 356/2; 250/220 SP [56]References Cited UNITED STATES PATENTS 7/1972 Johnston .356/2 5/1972Hobrough 356/2 Primary Examiner-Ronald L. Wibert Assistant Examiner-PaulK. Godwin Attorney-Homer Blair, Robert L. Nathans et [5 7] ABSTRACT Anautomatic stereoplotting system employing both a high speed primaryservosystem for inducing substantially instantaneous primary relativedisplacements between scanning pattems to eliminate detected parallax,and a more massive and slower reacting auxiliary servo system forinducing relative displacements between left and right stereophotographs being scanned. The auxiliary displacements of thephotographs replace the initial primary displacements of the scanningpatterns and a readout mechanism records measured elevations bycontinuously indicating the algebraic summations of both the primary andauxiliary displacements. A distribution circuit is provided fordistributing the displacements of the scanning patterns between thescanning systems for the left and right stereo photographs so as toeliminate the parallax from each photograph in proportion to the actualimage displacement on each photograph.

This invention is an improvement on the Automatic StereoplottingApparatus described in US. Pat. No.

3,677,645, filed Mar. 1, 1970.

7 Claims, 11 Drawing Figures vaoso AMPLIFIER [234 Tr-ss PHOTO PHOTO 33MULTIPLIER MULTIPLIER CORRELATHON 37 svs'rau 3B 3 39 46 ,4? 57 f i 3 5422 2a 52 IMAGE REGISTRATION ji AND T 1 PROFILING CONTROL STEREO SYSTEM55 PHOTOGRAPHS 53 r evemzcz FIELD FIELD Frames AND RELAY AND RELAYAMPLIFIER OPTICS LENSES LENSES OPTICS ea 26 l 21 I J United StatesPatent [1 1 [111 52,580

Hardy [451 Aug. 14,1973

CORRELATOR PMT PMT LEFT RIGHT '68 PHOTO PHOTO CRT CRT m 66 ZCARRIAGEPAIENTED MIG I4 I975 SHEET 2 BF 6 PAIENIEumuma 3.752.580

sum 5 or 6 GROUND PLANE PAIENIEBM 14 W8 SIIEEI 6 HF 6 LEFT VERTICALIFIG.8)

RIGHT x POSITION,

I50(FIG.7.)

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RIGHT VERTICAL FIG. 9.

DE ELECTION VOLTAGE CO R RELATOR CRT I Z CARRIAGE FIG. IO.

F|G.II.

X CARRIAGE STEREO INSTRUMENT HAVING DIFFERENTIALLY VARIED LEFT AND RIGHTPARALLAX ERROR SIGNALS FOR PRODUCING SCANNING PATTERN DISPLACEMENTSBACKGROUND OF THE INVENTION tain elevation and position measurements ofterrain imaged on a pair of stereographic photographs. The stereophotographs are positioned in a stereoplotting machine that produces foran operator a stereographic presentation of a particular area of theterrain imaged on the photographs. By inducing appropriate relativedisplacement of the photographs in a direction corresponding to thedirection of separation between the positions from which the photographswere taken, the operator registers image detail and eliminates zeroorder distortion in the stereo presentation. The magnitude ofdisplacement required to eliminate the distortion, commonly calledparallax, is proportional to the relative elevation of the actualterrain imaged on the viewed area of the photographs and isautomatically recorded by the stereoplotting machine. Simultaneouslyrecorded for the viewed area is its position in the photographs whichidentifies the relative position of the actual terrain. Thus, bycontinuously maintaining registration of the individually viewed imageareas, while systematically traversing the entire surface of the twophotographs, relative elevation and position informationis obtained forall the terrain imaged on the photographs.

Typically, the systematic traversal is accomplished by moving thephotographs on an x-y carriage relative to the optical viewing system.While controlling movement of the x-y carriage, the operatorcontinuously adjusts the horizontal displacement between the photographsso as to maintain image registration. Generally the operator is guidedduring the procedure by the well-known floating mark." This markcomprises some indicia such as light spots located at the optical axesof the stereo viewing system and when fused into a single spot in thestereo presentation appears to lie on the surface of the stereo terrainmodel only when the images are properly registered.

Even with the most modern instruments, manual stereoplotting is atedious and time consuming operation. The time requuired to manuallyprofile a typical stereo model is between 2 and 4 hours, depending onthe roughness of the terrain. When functioning to adjust the apparentheight of the floating mark by means of a hand or foot wheel, a humanoperator becomes part of a closed loop feedback system and is subject tosome basic limitations. For example, his response, i.e., the time delaybetween the perception of an error in the height of the floating markand its subsequent correction by means of the hand wheel, has a definiteminimum value making it necessary to reduce traversing speed in roughterrain.

A number of automatic stereoplotting systems have been developed forsimplifying the dual image registration procedure. Basically, most suchsystems scan homologous sections of the two photographs and convert thescanned graphic data into a pair of electrical video signals. By variouscorrelation and analyzation techniques, the video signals are used toproduce error signals representing certain types of distortion existingbetween the scanned image sections. The scanned sections are thenrendered congruent by image detail transformation produced in responseto the derived error signals. Usually, the x-parallax error signalindicative of terrain elevation is applied to a servomechanism thatcorrects zero order distortion by producing appropriate relativemovement between the stereo photo graphs or height adjustments of aviewing surface that intercepts a projection of the images. As notedabove, the magnitude of required x-parallax correction is directlyrelated to the relative elevation of the actual terrain and provides thecontour information necessary for topographic maps. One type oftopographic map which may be produced from this information is anorthographic map which is a type of map which has each point on the mapat the position it would occupy if it were photographed from a positiondirectly vertically above it.

The electro-mechanical servomechanisms utilized in automaticstereoplotting instruments, given suitable input, can respond morequickly than a human operator and consequently can substantially reducethe time required to profile a stereo model particularly one involvingrapid fluctuations of terrain height. The same servomechanisms, however,also introduce errors in the output information. Because the mechanicalassemblies controlled by the servomechanism are relatively massive, aninherent following error is introduced during periods requiring rapidacceleration. Some finite time period is required by the servomechanism,therefore, to effect corrective relative displacements in response to anx-parallax error signal derived from discrete scanned sections of thetwo photographs. The particu' lar image sections being scanned, however,are continuously changed by traversing movement of the x-y carriageretaining the photographs. Thus the elevation indicated by theinstantaneous position of the servo" mechanism does not correspondidentically to the x-y coordinate position of the image sections beingscanned. Rather, the instantaneous positions of the ser vomechanismrepresent the elevation of image sections. scanned a finite periodearlier. Because of this discrep ancy the elevation and positioninformation outputs continuously recorded by the automaticstereoplotting instrument do not exactly correspond.

The object of the invention, therefore, is to provide an improvedautomatic stereoplotting instrument that eliminates the problems notedabove.

CHARACTERIZATION OF THE INVENTION The invention is characterized by theprovision of an automatic stereoplotting system including an x-ycarriage for supporting a pair of stereographic photographs. A pair offixed cathode ray tubes produce scanning beams which are directedthrough and modulated by image detail retained in distinct areas of thestereographic photographs and drive motors selectively move the carriagein orthogonally related directions so as to change simultaneously anduniformly the areas being scanned. Image detail information extracted bythe scanning beams is converted into video analog signals which arecorrelated and analyzed according to conventional techniques producingan .r-parallax error signal indicative of x-parallax existing betweenthe image areas being scanned.

The parallax error signal is fed directly to a high speed instrumentservo whose loads are one input to the readout synchro and apotentiometer. Because the potentiometer and readout synchro have verylow mass, high acceleration with low torque requirements are possible.The output from the potentiometer is fed via a distribution circuit tothe x-deflection coils of the scanning system which deflect the scanningpatterns in the direction required to null the x-parallax signal.Voltage adjustments across the potentiometer are such that the synchrois advanced by an amount exactly representing the elevation change thatproduced the error. Thus, the synchro output indicates the trueelevation of the terrain being scanned. The distribution circuit assuresthat the scanning patterns for the left and right stereo photographs aredisplaced in a manner which eliminates the parallax from each photographin proportion to the actual image displacement on each photograph. Thevoltage from the potentiometer is also fed to the relatively slow speedz-carriage servo system which causes the carriage to move in thedirection required to mechanically null the scanning patterndeflections. This has the effect of generating signals at the input tothe high speed servo system which are opposite in polarity to theoriginal x-parallax signals, causing the output of the potentiometer torevert to zero as the zcarriage reaches the true mechanical null. Duringthe period in which the z-carriage servo is approaching mechanical nulland the high speed servo is reverting to its original zero outputcondition, their relative motions are cancelled in a differentialcoupling mechanism at the input to the readout synchro. Consequently,its position remains fixed and its output continues to reflect trueelevation. The invention features, therefore, xparallax correction byboth scanning pattern deflection and z-carriage produced photographdisplacement. Together, the two forms of correction provide both thequick response of scanning pattern deflection and the accuracy andincreased range of mechanical photograph displacement.

DESCRIPTION OF THE DRAWINGS These and other objects and features of theinvention will become more apparent upon a perusal of the followingdescription taken in conjunction with the accompanying drawings wherein:

FIG. 1 is a general block diagram illustrating the functionalrelationship of the main components of the apparatus;

FIG. 2 is a perspective schematic view of the image transformationmechanism 21 shown in FIG. 1;

FIG. 3 is a block diagram of the displacement control unit 103 shown inFIG. 2;

FIGS. 4-6 are diagrammatic representations illustrating operation of theinvention under a given set of conditions; I

FIGS. 7 and 8 illustrate how parallax distortions occur between left andright stereo views, and aid in an explanation as to why the circuit ofFIG. 10 is desirable;

FIG. 9 is a graph which illustrates the desired deflections for the leftand right scanning circuits depending upon the position of the Xcarriage in the Planimat;

FIG. 10 illustrates one embodiment of a distribution circuit which maybe utilized to distribute the displacements of the scanning patterns forthe left and right stereo photographs;

FIG. 11 illustrates one embodiment for connecting potentiometers RA andRB to the X carriage.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to FIG. 1 there isshown in block diagram form an image transformation mechanism 21retaining a pair of stereo photographic transparencies 22 and 23.Scanning beams 24 and 25 produced by, respectively, cathode ray tubes 26and 27 are directed toward the transparencies 22 and 23 by field andrelay lens assemblies 28, dichroic beam splitters 29 and objectivelenses 31. After passing through the transparencies 22 and 23 thescanning beams 24 and 25 are received by photo-multipliers 32 and 33that produce on lines 34 and 35, respectively, video analog signalsrepresenting the variable detail retained by the photographs. Betweenthe transparencies 22 and 23 and the photomultipliers 32 and 33 thescanning beams pass through lens systems including dichroic mirrors 36and blue light filters 37.

Also reflected through the transparencies 22 and 23 by the dichroicmirrors 36 is yellow light produced by light sources 38 and 39. Afterbeing modulated by the transparencies 22 and 23, the yellow light isdirected to a pair of eyepiece optical assemblies 41 and 42 by theobjective lenses 31, the dichroic beam splitters 29 and a pair ofmirrors 40 and 40'. The eyepiece optical assemblies 41 and 42 providefor a viewer in conventional manner a stereo presentation of the imagedetail retained by the transparencies 22 and 23.

A correlation system 44 receives the analog signals on lines 34 and 35after amplification in a video amplifier 43. The correlation system 44correlates the video signals producing on lines 45 and 46, respectively,x and y cross-correlation signals proportional to the levels ofcorrelatable image detail being scanned in the orthogonally related xand y directions in the photographs 22 and 23. Also produced on line 47is an orthogonal correlation signal proportional to the degree ofrelative image detail misregistration existing between the scannedpaths. The correlation system 44 does not, per se, form a part of thisinvention. However, circuits suitable for this application are disclosedin U. S. Pat. Nos. 2,964,644 and 3,145,303 and in U. S. application Ser.No. 839,940 ofJohn W. Hardy et al. filed July 8, I969.

The correlation signals on lines 45-47 are fed into an imageregistration and profiling control system 48 also not a part, per se, ofthis invention but described in detail in above noted U. S. applicationSer. No. 839,940.'

The control system 48 produces on lines 51 and 52, respectively,x-parallax error and traversing velocity control signals that areapplied to the image transformation and transport carriage system 21.Also produced are deflection control signals that are applied on lines58 and 59 to deflection coils of cathode ray tube 26 and on lines 61 and62 to deflection coils of cathode ray tube 27.

Generated in the image transformation system 21 on line 50 is a primarydisplacement control signal that is amplified in a push-pull amplifier53 and then combined in opposite polarities with the deflection signalson lines 58 and 61. Also supplied by the image transformation system 21are x and y coordinate position indieating signals on lines 54 and 55,respectively, and a measured elevation signal on line 56. The signals onlines 54-56 are all applied to a conventional recorder 57 that recordstheir information content in graphic form.

6 Shown in FIG. 2 is a schematic perspective view of the dual imagetransformation system 21 shown in FIG. I. The trans-formation system 21provides controlled movement of the photographic transparencies 22 and23 in orthogonally related x and y-coordinate directions. A y-carriage67 is mounted on rollers 68 'for movement alongparallel y-tracks 69supported by a frame 71. Similarly, an x-carriage 72 is mounted onrollers 73 for movement along x-tracks 74 supported by the y-carriage67. Movement of the y-carriage 67 is produced by rotation of a y-leadscrew 75 that engages the internally threaded collar 76. Rotation of thelead screw 75 is controlled by a y-servo motor 77 energized by thevelocity control signal on line 52. Similarly, movement of thex-carriage 72 along tracks 74 is produced by rotation of an x-lead screw78 also driven by a suitable x-servo motor 80. 3

A z-carriage 81 is mounted for vertical movement on z-lead screws 82supported by the x-carriage 72. Controlled vertical movement of thez-carriage81 is produced by z-servo motor 83 energized by the controlsignal on line 50 and coupled to the z-lead screws 82 by drive shaft andbevel gear assemblies 84. The photographic transparencies 22 and 23 aremounted, respectively, in photo carriages 86 and 87. Slidably engagingthe photo carriages 86 and 87 and providing mechanical coupling thereofto the z-carriage 81 are space rods 88 and 89. Opposite ends of thespace rods 88 and 89 terminate, respectively, in pivot connections 91and ball joint assemblies 92 mounted on the z-carriage 81. Theconnections 91 and 92 permit oppositely directed arcuate movement ofrods 88 and 89 in response to vertical movement of the z-carriage 81.This in turn produces relative rectilinear motion between thetransparencies 22 and 23 in the x-coordinate direction defined byx-rails 74 and ot'a sense determined by the direction of z-carriage 81movement. The image transformation mechanism 21 is a conventional unitmarketed under the trade name Planimat by the Carl Zeiss Company, ofOberkochen, Wurttemburg, Germany. The device is also related to similartransformation systems disclosed in the above noted U.S. Pat. Nos.2,964,644 and 3,145,303.

In response to appropriate energization of y-motor 77 the phototransparencies 22 and 23 move simultaneously with the y-carriage 67 ineither a plus or minus y-coordinate direction defined by y-tracks 69.The speed and direction of movement is determined by the velocitycontrol signal on line 52. Similarly, energization of x-lead screw 78produces simultaneous movement of the transparencies in either a plus orminus xdirection defined by the x-tracks 74. Thus, the mechanism 21provides selective uniform two dimensional movement of thetransparencies 22 and 23 relative to their respective scanning beams 24and 25 illustrated in FIG. 1. Conversely, vertical movement of thezcarriage 81 in response to energization of z-servo' motor 83 results inrelative movement between themselves as well as between thetransparencies and the scanning beams 24 and 25. As described below,this action of the z-servo motor 83 in combination with the rasterdeflections produced by the signal on line 50 aligns the beams 24 and 25(FIG. I) with homologous image detail in the transparencies 22 and 23.Consequently, registration is maintained between the image detail beingscanned and in the display provided by the eyepieces 41 and 42. Theaggregate amount of relative photograph displacement and scanningpattern deflection required to produce this registration is directlyrelated to the actual elevation of the terrain imaged on the sectionsofthe stereo photos being scanned.

In typical operation, the system shown in FIG. 1 is used to profile astereo model represented by the stereographic transparencies 22 and 23.For example, to profile automatically in the y-coordinate direction,ymotor 77 is driven at a predetermined velocity giving rectilinearmotion to y-carriage 67 and the transparencies 22 and 23 relative to thescanning beams 24 and 25. The x-motor 80 forms a part of a positioningservo, that holds the x-carriage 72 rigidly in the x-coordinatedirection. The system is thereby constrained to trace out a straightprofile in the y-dlirection and the xposition is selected by anautomatic stepping system (not shown) controlled, for example, by aconventional limit switch operated when the y-carriage 67 reaches oneedge of the stereo model. In response to actuation of the limit switch,the direction of rotation of y-motor 77 also would be reversed tothereby reverse the traversal direction of the y-carriage 67. Obviously,a reversal in roles ofthe x and y-motors would result in the tracing ofprofiles in the x-direction.

As a profile is being traced, a displacement unit 103 (FIG. 2)continuously responds to the x-parallax error signal on line 51 byproducing appropriate displace ments of the transparencies 22 and 23 andof the scanning rasters to eliminate x-parallaic and thereby provide adirect indication of terrain elevation. This operation is described ingreater detail below. Simultaneously, yparallax and other first orderdistortions are corrected in response to other error signals produced bythe control system 57 on lines 58, 59, 61 and 62. Consequently, a viewerutilizing the eyepiece optics 41 and 42 is provided with a correctedstereo presentation of the image scene retained by the transparencies 22and 23. The correction of y-parallax and other distortions can beachieved in various ways. However, a preferred method involvescontrolled relative distortion of the cathode ray tube rasters asdisclosed in US Pat. No. 3,432,674 of Gilbert L. Hobrough issued Mar.II, 1969.

During a profiling operation, a y-encoder 101 (shown in FIG. 2) isdriven by the y-lead screw to produce an output on line 55 thatidentifies the position of the y-carriage 67 on track 69. Similarly, anx-encoder 102 is driven by x-lead drive screw 78 to provide on line 54 asignal identifying the position of the x-carriage 72 on track 74. Thepositions of the x-carriage 72 and the ycarriage 67 also establish thepositions of the transparencies 22 and 23 with respect to the fixedoptical axes of the lens assemblies 28 and 36. Thus, the signals onlines 54 and 55, respectively, identify x and y coordinate positions ofpoints in the transparencies 22 and 23 aligned with the optical axes.Simultaneously produced by the displacement control unit 103 on line 56is an output proportional in value to the combined relativedisplacements of the photographs 22 and 23 and of the scanning beams 24and 25. As noted above, the displacements required to produceregistration of the scanned sections in the transparencies 22 and 23 isdependent upon the relative elevation of the actual terrain imagedthereon. Therefore, the output on line 56 is indicative of thatelevation. The related outputs on lines 54-56 are applied to therecorder 57 (FIG. 1) which records the information providing a graphicrecord of terrain elevations at particular coordinate positions in thetransparencies 22 and 23.

As noted above, when profiling photographic areas representingrelatively steep terrain, the relatively large mass of the z-carriage 81prevents the z-servo motor 83 from maintaining accurate registrationbetween areas scanned in the photographs 22 and 23. This problem isobviated in the present invention by the displacement control unit 103(FIG. 2). As described below in connection with FIG. 3, the displacementcontrol unit 103 provides both the quick response of electronicallyinduced scanning raster displacement and the range and accuracy ofphysical photograph displacement.

As shown in FIG. 3, the unit 103 includes a primary servo motor 110 thatis coupled to a potentiometer 111 by engaged gears 112 and 113 keyed,respectively, to a motor shaft 114 and a potentiometer shaft 115.Connected by variable resistors I16 and 117, respectively, to inputterminals of the potentiometer 111 are positive and negative voltagesources 118 and 119. The variable output voltage of the potentiometer111 is applied to the signal line 50 also shown in FIGS. 1 and 2.

Also receiving the primary control signal on line 50 is the z-servomotor 83 shown in FIG. 2. The shaft 121 of the z-motor 83 is operativelycoupled to z-table drive shafts 84 as described above and to adifferential coupling mechanism 122 in the control unit 103. Alsooperatively coupled to the differential coupling 122 is a shaft 123driven by the motor shaft 114 via the engaging gears 112 and 124. Theoutput shaft 125 of the differential coupling mechanism 122 drives areadout synchro 126, the signal output of which appears on line 56 alsoshown in FIGS. 1 and 2.

To explain the operation of the control system shown in FIG. 3,reference is now made to FIGS. 4-6. These figures illustrate indiagrammatic form the effect produced on the photographs 22 and 23 andon the scanning beams 24 and 25 by the control system under a given setof hypothetical conditions. The diagrams shown in FIGS. 4-6 are relatedto each other in both a geometrical and a temporal sense. For reasons ofsimplicity only the right photographic transparency 23 and the rightscanning beam 25 are represented in each of FIGS. 4-6, it beingunderstood that related reactions are experienced by the leftphotographic transparency 22 and the left scanning beam 24. It should befurther noted that the relative dimensions of the photograph 23, thescanning rasters and the various displacements illustrated in FIGS. 4-6were selected for reasons of clarity and do not accurately reflect thedimensional relationship that would exist between these items in apractical application.

With reference now to FIG. 4, assume that at time t the right photograph23 is positioned as shown relative to the y-direction center line A ofthe z-carriage 81 shown in FIG. 2. Assume also that the y-carriage 67 ismoving the photograph 23 relative to the fixed right cathode ray tube 27(FIG. 1) in the y-direction indicated by arrow B and that the rightscanning beam is tracing a scanning pattern 131. In addition, assumethat the upper and lower portions of the photograph 23 retain,respectively, imagery of substantially-flat terrain but of differentelevation separated by a vertical embankment represented by dotted lineC. Under these conditions the scanning pattern 131 will be movingrelative to the surface 'of the photograph 23 along a rectilinear pathrepresented by the dotted line D. Assume finally that at time t the leftand right photographs 22 and 23 are in perfect registration; i.e., thescanning beams 24 and 25 are simultaneously scanning homologous imagedetail in the two photographs so that no parallax error signal ispresent at the output of the image registration system 48 on line 51(FIG. 1).

' As the scanning raster 131 moves across line C, the correlation system44 (FIG. 1) detects the change in elevation of the imaged terrain andgenerates a raw error signal on line 47. This in turn generates anxparallax error signal on output line 51 of the registration system 48.The servo motor (FIG. 3) is energized by the x-parallax error signal andinduces rotation of the potentiometer shaft via the mating gears 112 and113. Rotation of the shaft 115 interrupts the balance in thepotentiometer 111 producing an output signal on line 50 that isdifferentially applied to the xdeflection signal lines 58 and 61 afteramplification in the push-pull amplifier 53 (FIG. 1). Application ofthese signals to the deflection coils ofcathode ray tubes 26 and 27induces relative deflections of the scanning beams 24 and 25 in sensesthat tend to eliminate the xparallax detected by the correlation system44. This result is diagrammatically illustrated in FIG. 4 by the dottedsquare 132 that represents the position of the right scanning patternafter a deflection of the right scanning beam 25 in a negativex-direction at time 1,. Assuming that at time t, registration againexists, the displacement distance d required to establish registrationrep resents the change in elevation of the terrain imaged on oppositesides of line C. A measurement of the magnitude and sense of thatdisplacement and, therefore, of the relative change in elevation isproduced on line 56 by the readout synchro 126 (FIG. 3) which is alsodriven by the servo motor 110 via the mating gears 112 and 124 and thedifferential coupling mechanism 122. Because the potentiometer 111 andthe readout synchro 126 are of relatively low mass, the servo motor 110is able to substantially instantaneously produce corrected outputs onlines 50 and 56 in response to the reception of xparallax error signalson line 51. Therefore, continuous registration is maintained byappropriate primary deflection of the scanning patterns traced by thebeams 24 and 25. Conversely, the relativel large mass of the z-carriage81 (FIG. 2) causes an inherent delay in the response of the z-servomotor 83 to control signals on line 50. This delayed response isrepresented in the simplified example of FIG. 4 by the assumption thatat time 1 no movement of the carriage 81 has occurred.

AT time t,, however, zmotor 83 has responded to the output signal online 50 by introducing displacement of the right photograph 23 adistance d in a positive x-direction as diagrammatically illustrated inFIG. 5. The relative x-direction positions of the scanning patterns attimes t, and t, are also shown in FIG. 5 and it is again understood thatrelated displacements are made on left photograph 22. Since movement ofphotograph 23 relative to the right scanning beam 25 during period t t,tends to eliminate the registration assumed at time t,, an x-parallaxerror signal is again produced on line 51 by the image registrationsystem 48. The

.tern 133 during time t,--t exactly equals the deflection d of thephotograph 23 during that'period so as to retain their existing relativepositions and accordingly maintain registration.

During the period between t ft the movement of the z-motor 83 alsoactivates the differential coupling 122. This action, however, iscounteracted by the simultaneous activation of the coupling mechanism122 by the servo motor 110 responding to the x-parallax error signal online 51. The mechanical coupling between the various components is suchthat for the assumed case of equal displacements d and d of,respectively, the photograph 23 and the scanning pattern 133, theposition of the coupling mechanisms output shaft 125 remains unchanged.Thus, the output of readout synchro 126 on line 56 remains constant toaccurately reflect the uniform elevation assumed to exist for theterrain imaged above line C of the photograph 23. lt will be obviousfrom the above that the output of the readout synchro I26 continuouslyreflects the algebraic summation of the displacements experienced by thephotograph 23 and the right scanning beam 25. Furthermore, thatsummation accurately represents the total relative displacement requiredto establish registration and, accordingly represents the elevation ofthe terrain imagery being scanned. At time t for example, the synchrooutput reflects the combined displacements d and d of, respectively, theright scanning beam 25 and the right photograph 23. Obviously, thattotal displacement d,+d corresponds in magnitude to the originalscanning beam displacement d that established registration at time t,.

As diagrammatically illustrated in FIG. 6, the z-servo motor 83continues to respond to the potentiometer output on line 50 during timeperiod !,-t;, effecting further displacement of the right photograph 23in a positive x-direction. Finally, at time t the right photograph 23reaches the relative position shown in FIG. 6. Again, themisregistration induced by this movement results in the generation ofx-parallax error signals on line 51 and accompanying energization of theservo motor 110 (FIG. 3). The resultant rotation of the potentiometershaft 115 reduces the potentiometer output on line 50. Consequently, theright scanning beam 25 is also deflected in a positive x-directionduring period t -t At time 1 the right scanning pattern 134 reaches therelative position illustrated in FIG. 6, which position corresponds inthe x-direction to its original nulled position assumed at time t Atthat time the potentiometer 111 is in its neutral position and output onsignal line 50 is eliminated. The z-servo motor 83 is thereforedeenergized and displacement thereby of the right photograph 23discontinued. As above, the magnitude of the xdirection displacement dexperienced by the right photograph 23 during time period 2 -4 exactlycorresponds to the x-direction displacement d experienced by the rightscanning beam 25 during that period. Thus, the movement of the motorshafts 114 and 121 are again cancelled by the differential couplingmechanism 122 and the output shaft 125 remains in a constant position.

Reviewing the operations schematically diagrammed in FIGS. 4-6, thesystem responds to the imaged terrain elevation .change assumed atdotted line C (FIG. 4) by inducing substantially instantaneous relativedeflections of the scanning beams 24 and 25. The size and direction ofthe beam deflections are such as to eliminate the parallax introduced bythe elevation change. These deflections are represented in FIG. 4 by thedistance 11,, it again being understood that the left scanning beam 24experiences a related deflection. The value and sense of the deflectiondistance d,, therefore, is a measurement of the magnitude and sense ofthe elevation change-assumed at line C and, as described above, a directindication of that measurement is provided by the readout synchro 126 online 56 (FIG. 3).

During time period 2 -1 the initially induced primary deflection of thescanning beams 24 and 25 is completely eliminated and replaced bysimultaneously induced physical displacements of the photographs 22 and23. Thus at time l the finally induced auxiliary displacement d of theright photograph 23 corresponds exactly in size but is of opposite senseto the initially induced primary deflection d, of the right scanningbeam 25. During the period t,-t when both primary deflection of thescanning beams and auxiliary displacement of the photographs areoccurring, the differential coupling mechanism 122 provides an output onshaft 125 representing the algebraic summation of both types of relativedisplacement. Thus, the output of the readout synchro 126 continuouslyindicates the total magnitude of relative displacement required toeliminate parallax between scanned portions of the two photographsandconsequently of the relative elevations of the terrain imaged thereon.

Again, it will be understood that the conditions described in connectionwith FIGS. 4-6 were assumed for reasons of simplifying an explanation ofthe inventions operation. In light of this explanation, however, themanner in which the disclosed system responds to con ditions existing ina more practical application will be obvious. By employing both theprimary and auxiliary relative displacements described above, thepresent invention provides the substantially instantaneous re sponse ofelectronically induced raster deflection in addition to the overallrange and accuracy of physically induced photograph displacement.

A distribution circuit may be provided for distributing thedisplacements of the scanning patterns between the scanning systems forthe left and right stereo photographs so as to eliminate parallax fromthe photograph or photographs in proportion to the actual imagedisplacement in each photograph. FIGSJ7 and 8 illustrate how parallaxoccurs between left and right stereo views, and aid in an understandingas to why a distribu tion circuit, such as illustrated in FIG. 10, isdesirable.

FIG. 7 illustrates a situation wherein a'right stereo view of terrain isphotographed through a lens system onto photograph 142. A left stereophotograph 144 of the same terrain is also taken. In an orthographicmap, point P on the terrain would appear as if it were photographed froma vertical position and would appear in the ground plane at point P.However, as photographed from the right stereo view on photo graph 142,point P is imaged on the photograph at point B, and appears to belocated on the ground plane at point B. Conversely, in the left stereophotograph point P is imaged on the photograph A, and appears to belocated on ground plane at point A. If images from photographs 142 and144 are examined in a stereo instrument such as the Zeiss Planimat, thenpoint P will appear at Point A in the left stereo view and at point B inthe right stereo view. The distance along the X axis between points Aand B represents x-parallax. To eliminate parallax during operation ofthe Zeiss Planimat, photograph 142 is moved slightly to the left adistance AXB by movement of the Z carriage, and point B is projectedonto the ground plane at point P, as illustrated in dashed lines. Also,photograph 144 is moved slightly to the right a distance AXA, and pointA is projected onto the ground plane at point P, as illustrated indashed lines; With these corrective movements of the stereo photographsno parallax distortion will then exist between the projection of pointsA and B. The measurement of parallax, as indicated by the X distancebetween points A and B, enables the determination of the actual heightof point P above the ground plane and also the production of anorthographic map.

Now consider the case illustrated by FIG. 8 wherein a point P on theground terrain is photographed on a left stereo photograph 148 and aright stereo photograph 146. In this instance, point P is directlyvertically below the position at which photograph 148 is taken.Photograph 148 presents point P in an orthographic view, and whenutilized in a stereo instrument such as the Zeiss Planimat photograph148 would project point P to point P in the ground plane. On the otherhand, photograph 146 has an image of point P at B, and point P appearsto be located at point B on the ground plane.

If the parallax distortion between points B and P were attempted to beremoved by an equal and opposite movement of each photograph (as was thecase in FIG. 7), then a movement of photograph 148 to the right by adistance AXA would result in a projection of point A down to point P inthe ground plane. Likewise, a movement of photograph 146 to the left bya distance AXB would result in a projection of point B down to point P.Thus, in the attempted correction for an orthographic view, point Pwould be shifted to point P and would result in an erroneousorthographic map. It is evident that in the special case when theprojection of photograph 148 presents the correct orthographic view, allthe correction for parallax distortion should be accomplished by ashifting of photograph 146. In this instance if point B in photograph146 were shifted over to position C then point P would be properlyprojected in the orthographic view to point P in the ground plane. Theopposite would be true if the terrain were photographed directly beneathphotograph 146. In that instance all of the parallax distortion shouldbe corrected for in the projection of photograph 148.

Selected lateral movements in the X direction of either the left orright stereo photographs to eliminate parallax is accomplishedautomatically in a stereo instrument such as the Zeiss Planimat. If amiddle point in the terrain illustrated by the stereo photographs werebeing examined (as illustrated in FIG. 7), then the space rods 88 and 89of the Planimat would assume a position as illustrated in FIG. 2 whereineach of the rods 88 and 89 are positioned at approximately the sameangle relative to the Z carriage 81. In that position, a movement of theZ carriage would result in equal and opposite movements of the stereophotographs 22 and 23. If a left end point in the terrain directly underthe left stereo photograph was being examined (as illustrated in FIG. 8)then the left space rod 88 would assume a vertical position and theright space rod 89 would assume an angular position relative to the Zcarriage approximately equal to the angle at which that left endposition of the terrain was originally photographed onto rightphotograph 146. A movement of the Z carriage 81 to eliminate parallaxdistortion would result in photograph 22 remaining stationary andphotograph 23 moving alongthe X axis to eliminate the parallax. Ifaright end point in the terrain located vertically under the right stereophotograph were being examined then the right space rod 81 would assumea vertical position and the left space rod 88 would assume an angularposition relative to the Z carriage approximately equal to the angle atwhich the terrain was originally photographed onto the left photograph.In that position any movement of the Z carriage to eliminate parallaxwould result in a lateral movement along the X axis of only the leftstereo photograph.

The high speed servo system should also be provided with a means wherebythe x displacement of the scanning patterns is distributed between thescanning systems for the left and right stereo photographs so as toeliminate parallax from the photograph or photographs in proportion tothe image displacement in each photograph before corrections have beenmade by the low speed Z servo 83. FIG. 9 is a graph which illustratesthe desired deflections for the left and right scanning circuitsdepending upon the position of the X carriage in the Planimat. Theposition of the X carriage determines what portions of the terrain alongthe X axis are being examined, and is indicative of the distribution ofparallax between the stereo photographs. Point on the graph is theposition of the X carriage at which each stereo photograph parallax atpoint P is equally distributed in. Such a situation is illustrated inFIG. 7. Accordingly, the X deflections in the left and right scanningcircuits should be equal and opposite to compensate for parallax. Asshown by the graph a positive voltage is applied to X deflection coilfor the left scanning tube, and an equal but negative voltage is appliedto the X deflection coil for the right scanning tube. Point 152 in FIG.9 illustrates the voltage which should be applied to the left and rightscanning tubes to compensate for parallax in a position as illustratedby FIG. 8. It will be obvious that the differences in relativedisplacements between point P and the photos 142 and 144 illustrated inFIGS. 7 and 8 result from and are proportional to the degree of Xdirection movement of the X carriage 72 before correction is achieved bythe slow speed Z servo 83. To instantaneously correct parallax for thecase illustrated by FIG. 8, the scanning pattern of the left scanningtube would not be deflected at all, and the scanning pattern for theright stereo photograph would be deflected by a large negative amount toeliminate any parallax. Position 154 on the graph illustrates thecorrect deflection voltages for the situation opposite to thatillustrated in FIG. 8 wherein the point in the terrain being examined isdirectly vertically below the right stereo photograph. Again the changein displacement would be a result of and proportional to the degree of Xcarriage movement in a direction opposite to that which produced thedisplacements illustrated in FIG. 8. In that situation the scanningpattern for right tube would not be deflected, and the scanning patternfor the left tube would be deflected by a large positive voltage. Theactual voltage to be applied to the deflection coils of the left andright scanning tubes is dependent upon the distance between thepositions at which the left and right stereo photographs were taken, andthe model magnification of the Zeiss Planimat which is in turn dependentupon the focal length of the lens system in the Planimat and theprojection distance of the Planimat.

FIG. illustrates one embodiment of a distribution circuit which may beutilized to distribute the displacements of the scanning patterns forthe left and right stereo photographs. The output of potentiometer 111on line 50 (FIG. 3) is applied to a distributing circuit consisting oftwo variable potentiometers 160 and 162. The voltage on line 50 isapplied directly to one side of potentiometers 160 and 162 through thevariable gain amplifier 164. It is also inverted by an operationalamplifier 170 and applied to the other side of potentiometers 160 and162. The voltage across potentiometer 160 is proportional to themeasured parallax in the left stereo view, and is applied via adeflection amplifier 166 to the X deflection coil of the left scanningtube 168. The voltage across the second potentiometer 162 isproportional to the measured parallax in the right stereo view, and isapplied via deflection amplifier 171 to the deflection coil for theright scanning tube 172. The resistances of potentiometers 160 and 162may be differentially varied in accordance with the X position of the Xcarriage in a manner as illustrated in FIG. 11. The X carriage 72 has acable attached to it which runs to pulley 174. Pulley 174 rotates commonshaft 176 which is connected to potentiometers 160 and 162. Thus,angular positions of the pulley 174 and shaft 176 measure the X positionof the X carriage 72. Potentiometers 160 and 162 are connected inopposite directions to shaft 176 such that when shaft 176 is rotated inone direction, one of the two potentiometers will have its resistanceincreased and the other potentiometer will have its resistancedecreased. Rotation in the opposite direction will have the oppositeresult. This differential coupling relationship between the pulley 174and the potentiometers I60 and 162 is schematically shown also by dashedlines in FIG. 10. In this manner the voltage on line 50 isdifferentially distributed in potentiometers 160 and 162 to the Xdeflection coils for the left and right scanning tubes in dependenceupon the X position of the X carriage.

Referring back to FIG. 9, when the X carriage assumes position I52,potentiometer 160 will deliver zero voltage to the X deflection coil forthe left scanning tube, and potentiometer 162 will deliver a negativevoltage proportional to the total X parallax to the X deflection coilfor the right scanning tube. Likewise, when the X carriage assumesposition 154 of FIG. 9 potentiometer 160 will deliver a positive voltageproportional to the total X parallax to the X deflection coil for theleft scanning tube, and potentiometer 162 will deliver zero voltage tothe X deflection coil for the right scanning tube. In the middleposition of the X carriage illustrated at point 150 in FIG. 9,potentiometer 160 will deliver a positive voltage to the X deflectioncoil for the left scanning tube, and potentiometer 162 will deliver anequal but negative voltage to the X deflection coil for the rightscanning tube.

Referring to the circuit of FIG. 10, two adjustments are included toadjust for varying parameters under which the left, and right stereophotographs are taken and in the Zeiss Planimat. A variable resistance173 is provided to adjust the voltage across the potentiometers a'nd 162such that potentiometers 160 and 162 will respectively produce zerovoltages when the left and right space rods are respectively vertical.The variable amplifier 164, the gain of which is adjustable, is providedto vary the slopes of the voltage lines illustrated in FIG. 9 for theleft and right tubes. The value at which variable amplifier 164 is setdepends upon the distance between the positio'nat which the left andright stereo photographs were taken, andthe magnif cation utilized inthe Planimat which is in turn dependent upon the focal length of thelens system and the projection distance of the Plani'mat.

Although the preferred embodiment of the distribution circuit includestwo potentiometers, an alternative circuit might be utilized which hasonly one variable potentiometer mechanically connected to the X canriage. The one potentiometer would control two circuits. One circuitwould produce a higher voltage in response to an increase in resistanceof the potentiometer, and the second circuit would produce a lower ornegative voltage in response to an increase in resistance of thepotentiometer. Alternatively, the position of the X carriage might bemeasured with a variable inductance, a variable capacitance, or someother variable parameter.

Obviously, many modifications and variations of the present inventionare possible in light of the above teachings. It is to be understood,therefore. that the invention can be practiced otherwise than asspecifically described. I

I claim:

l. A'stereo instrument for examining left and right stereo views of anobject and for determining parallax in said left and right stereo viewsand comprising:

a. a left scanning system for scanning different points in said leftstereo view and for producing a signal indicative of the image detail ineach scanned point;

b. a right scanning system for scanning different points in said rightstereo view and for producing a signal indicative of the image detail ineach scanned point;

e. means for moving said left and right stereo views along anaxiswherebydifferent points in said left and right stereo views along saidaxis may be examined;

d. means for measuring the position of said left and right stereo viewsalong said axis;

e. correlator means for correlating said signals from said left'andright scanning systems to detect parallax between said left andrightstereo views, and for producing aparallax error signal indicativeof said parallax;

f. rn'eans, res"ponsive to said measuring means, for distributing saidparallax error signal into left and rightparallax error signals havingmagnitudes that vary differentially depending upon the positions ofsaid-left and right stereo views along said axis, whe'rebythe leftandright parallax error signals are indicative of the amount of parallaxpresent in each view;

g. means, responsive to said left parallax error signal, for displacingsaid left scanning system along said axis a distance dependent on themagnitude of said left crror signal relative to the left stereo view andin a direction tending to reduce the parallax present in the left stereoview; and

h. means, responsive to said right parallax error signal, for displacingsaid right scanning system' along said axis a distance dependent on themagnitude of said right error signal relative to the right stereo viewand in a direction tending to reduce the parallax present in the rightstereo view.

2. Apparatus as set forth in claim 1 and wherein:

a. said moving means includes a carriage which is movable along saidaxis and on which said left and right stereo views are mounted; and

b. said measuring means includes a potentiometer means mechanicallycoupled to said carriage so that the resistance of said potentiometermeans changes as said carriage is moved along said axis.

3. Apparatus as set forth in claim 2 wherein said potentiometer meansincludes first and second potentiometers, said first and secondpotentiometers being mechanically coupled to said carriage means so thatmovement of said carriage means along said axis in a first directionwill cause the resistance of said first potentiometer to increase andthe resistance of said second potentiometer to decrease, and whereinmovement of said carriage along said axis in a direction opposite saidfirst direction will cause the resistance of said first potentiometer todecrease and the resistance of said second potentiometer to increase.

4. Apparatus as set forth in claim 3 wherein said stereo instrumentincludes:

a. a low speed servo system responsive to said parallax error signal forrelatively displacing said left and right stereo views along said axisto reduce parallax between said left and right stereo views;

b. a high speed servo system, complementary to said low speed servosystem, for responding quickly to said parallax error signals to reduceparallax between said left and right stereo views, said high speed servosystem including said means for displacing said right scanning systemand said means for displacing said left scanning system.

SQApparatus as set forth in claim 1 wherein said stereo instrumentincludes:

a. a low speed servo system responsive to said parallax error signal forrelatively displacing said left and right stereo views along said axisto reduce par allax between said left and right stereo views;

b. a high speed servo system, complementary to said low speed servosystem, for responding quickly to said parallax error signals to reduceparallax between said left and right stereo views, said high speed servosystem including said means for displacing said right scanning systemand said means for displacing said left scanning system.

6. Apparatus as set forth in claim 5 wherein:

a. said moving means includes a carriage which is movable along saidaxis and on which said left and right stereo views are mounted; and

b. said measuring means includes a potentiometer means mechanicallycoupled to said carriage so that the resistance of said potentiometermeans changes as said carriage is moved along said axis.

7. Apparatus as set forth in claim 6 wherein said potentiometer meansincludes first and second potentiometers, said firstand secondpotentiometers being mechanically coupled to said carriage means so thatmovement of said carriage means along said axis in a first directionwill cause the resistance of said first potentiometer to increase andthe resistance of said second potentiometer to decrease, and whereinmovement of said carriage along said axis in a direction opposite saidfirst direction will cause the resistance of said first potentiometer todecrease and the resistance of said second potentiometer to increase.

x a: i a

1. A stereo instrument for examining left and right stereo views of anobject and for determining parallax in said left and right stereo viewsand comprising: a. a left scanning system for scanning different pointsin said left stereo view and for producing a signal indicative of theimage detail in each scanned point; b. a right scanning system forscanning different points in said right stereo view and for producing asignal indicative of the image detail in each scanned point; c. meansfor moving said left and right stereo views along an axis wherebydifferent points in said left and right stereo views along said axis maybe examined; d. means for measuring the position of said left and rightstereo views along said axis; e. correlator means for correlating saidsignals from said left and right scanning systems to detect parallaxbetween said left and right stereo views, and for producing a parallaxerror signal indicative of said parallax; f. means, responsive to saidmeasuring means, for distributing said parallax error signal into leftand right parallax error signals having magnitudes that varydifferentially depending upon the positions of said left and rightstereo views along said axis, whereby the left and right parallax errorsignals are indicative of the amount of parallax present in each view;g. means, responsive to said left parallax error signal, for displacingsaid left scanning system along said axis a distance dependent on themagnitude of said left error signal relative to The left stereo view andin a direction tending to reduce the parallax present in the left stereoview; and h. means, responsive to said right parallax error signal, fordisplacing said right scanning system along said axis a distancedependent on the magnitude of said right error signal relative to theright stereo view and in a direction tending to reduce the parallaxpresent in the right stereo view.
 2. Apparatus as set forth in claim 1and wherein: a. said moving means includes a carriage which is movablealong said axis and on which said left and right stereo views aremounted; and b. said measuring means includes a potentiometer meansmechanically coupled to said carriage so that the resistance of saidpotentiometer means changes as said carriage is moved along said axis.3. Apparatus as set forth in claim 2 wherein said potentiometer meansincludes first and second potentiometers, said first and secondpotentiometers being mechanically coupled to said carriage means so thatmovement of said carriage means along said axis in a first directionwill cause the resistance of said first potentiometer to increase andthe resistance of said second potentiometer to decrease, and whereinmovement of said carriage along said axis in a direction opposite saidfirst direction will cause the resistance of said first potentiometer todecrease and the resistance of said second potentiometer to increase. 4.Apparatus as set forth in claim 3 wherein said stereo instrumentincludes: a. a low speed servo system responsive to said parallax errorsignal for relatively displacing said left and right stereo views alongsaid axis to reduce parallax between said left and right stereo views;b. a high speed servo system, complementary to said low speed servosystem, for responding quickly to said parallax error signals to reduceparallax between said left and right stereo views, said high speed servosystem including said means for displacing said right scanning systemand said means for displacing said left scanning system.
 5. Apparatus asset forth in claim 1 wherein said stereo instrument includes: a. a lowspeed servo system responsive to said parallax error signal forrelatively displacing said left and right stereo views along said axisto reduce parallax between said left and right stereo views; b. a highspeed servo system, complementary to said low speed servo system, forresponding quickly to said parallax error signals to reduce parallaxbetween said left and right stereo views, said high speed servo systemincluding said means for displacing said right scanning system and saidmeans for displacing said left scanning system.
 6. Apparatus as setforth in claim 5 wherein: a. said moving means includes a carriage whichis movable along said axis and on which said left and right stereo viewsare mounted; and b. said measuring means includes a potentiometer meansmechanically coupled to said carriage so that the resistance of saidpotentiometer means changes as said carriage is moved along said axis.7. Apparatus as set forth in claim 6 wherein said potentiometer meansincludes first and second potentiometers, said first and secondpotentiometers being mechanically coupled to said carriage means so thatmovement of said carriage means along said axis in a first directionwill cause the resistance of said first potentiometer to increase andthe resistance of said second potentiometer to decrease, and whereinmovement of said carriage along said axis in a direction opposite saidfirst direction will cause the resistance of said first potentiometer todecrease and the resistance of said second potentiometer to increase.